Androgen receptor plays a significant role in prostate carcinogenesis and its overexpression and aberrant activation are considered to be the underlying cause for the development of castrationresistant tumors, which at present defy any effective treatment. As a transcriptional factor, androgen receptor is involved in the assembly of transcriptional complex including coactivators on the target genome site. One special class of coactivators are histone modifying enzymes and the best understood are histone acetylases. A newly emerging class is histone demethylase, which serves to remodel the chromatin surrounding the androgen receptor binding site. They are thus both transcriptional coactivator and epigenetic regulator. The present proposal is based on our identification of a new histone demethylase with all the hallmarks of a strong coactivator of androgen receptor and is overexpressed in prostate cancer. It enhances androgen response, accelerates cell cycle progression, and exhibits a substrate specificity different from the known histone demethylases. Intriguingly, it is regulated by growth factor and is phosphorylated by tyrosine kinases. The enzyme is cell cycle regulated but also regulates cell cycle. Based on these preliminary observations, we wish to elucidate its biochemical properties as a demetylation enzyme, its regulation as a signal transducer, and its biological effects as an androgen receptor coactivator. Its potential as a biomarker and/or a target for therapy will also be evaluated.